Multi-blade cleaners are frequently used with belt conveyors in mining and mineral storage operations and other such applications; a multi-blade device is often used as a secondary cleaner that scrapes the return run of the conveyor belt to remove material that would otherwise adhere to its surface. Secondary cleaners usually supplement a single-blade or multi-blade cleaner that scrapes material from a part of the conveyor belt backed up by the head pulley. Conveyor belt cleaners, primary and secondary, usually operate in an environment that can only be described as hostile. The working conditions are frequently wet, dirty, and even corrosive. Continuing maintenance activity is a necessity due to inevitable wear on the cleaner blades, but is often rendered difficult by limited access space as well as the aforementioned adverse working conditions. In excessively wet or corrosive environments, maintenance is made more difficult by corrosion of metal mounting bolts, clamps, and the like. All of these difficulties are likely to be present in mining operations and also in industrial applications.
A secondary cleaner for a belt conveyor is likely to encounter substantial problems from shock forces applied to the cleaner blades. When large pieces of the conveyed material or debris, clinging to the conveyor belt, engage a cleaner blade, they may stress the blade or its support severely. The cleaner blades are also subject to impact damage from repeated engagement with joints between individual segments of the conveyor belt. Repeated shocks and impacts of this kind may lead to shutdown for repair or replacement of belt cleaner components, a time consuming and expensive procedure. Thus, it is important to minimize or avoid shock damage to the components of a secondary conveyor belt cleaner as well as to compensate for the inevitable wear on the belt cleaner blades due to continuing normal operation. Multi-blade cleaners are often preferred, in secondary cleaners because a multi-blade construction limits many stresses to only one blade of several, but an elongated continuous blade may sometimes be used in a secondary cleaner.
Effective and efficient conveyor belt cleaners that utilize a torsion bias mechanism to maintain the cleaner blades in engagement with the conveyor belt are disclosed in U.S. Pat. No. 4,533,036 issued to James R. Gordon Aug. 6, 1985. Both primary and secondary belt scrapers are disclosed. Those conveyor belt cleaners, however, have the disadvantage that replacement of individual cleaner blades or blade support arms may require appreciable down-time because the blades or their supports are keyed to the torsion biased shaft. The blade support arms utilized in the secondary cleaners shown in that patent may be made of inexpensive steel rod with molded resin joints; such steel rods may be undesirable, in wet and corrosive environments, due to excessive corrosion.
Other secondary conveyor belt cleaner arrangements are described in two United States patents to R. T. Swinderman, U.S. Pat. No. 4,643,293 issued Feb. 17, 1987 and U.S. Pat. No. 4,917,231 issued Apr. 17, 1990. In those two patents support arms molded of resilient resins such as polyurethane are employed in secondary type belt cleaners. Because the support arms are made entirely of resilient molded resin, they are not unduly prone to corrosion. In the later U.S. Pat. No. 4,917,231, the disclosed blades are designed to maintain a constant "cleaning angle" at the blade/belt interface despite blade wear. These blade support arms of resilient material must be made large enough to withstand belt pressure and torsion forces; stiff support arms (e.g. metal) can be thinner so that there is less material buildup on the arms.
Other secondary belt cleaners are disclosed in Gordon U.S. Pat. No. 4,854,443, issued Aug. 8, 1989. Each conveyor belt cleaner disclosed in that patent has cantilever blade support arms that utilize a keyed interference fit for a firm but displaceable mounting of the fixed end of the arm on a support. That patent provides internal reinforcements in either or both ends of each blade support arm, affording a marked improvement in durability.
One problem with secondary belt cleaners that has not received adequate recognition derives from the use of unduly flexible, resilient support arms. Some limited resilience in a secondary belt cleaner is necessary to accommodate belt joints and heavy, clinging, localized accumulations on the belts. But if each blade is readily displaceable independently of the others, as is often the case in prior constructions, undue displacement and vibration may reduce efficiency undesirably.